Apparatus for mapping a static magnetic field

Abstract

Apparatus for mapping a static magnetic field is provided. A liquid sample is positioned in a magnetic field probe adapted to generate an alternating magnetic field and for measuring an induced signal from the sample as a result of being exposed to the alternating magnetic field. The induced signal from the sample is measured at discrete points along a helical path located within the static magnetic field. Axial and radial shim coils can be positioned within the static magnetic field and the current directed to the coils can be controlled as a result of the field mapping results in order to homogenize the static magnetic field.

We claim: 
     
       1. Apparatus for mapping a static magnetic field generated by a static magnet which comprises: a liquid sample mounted on a magnetic field probe adapted to generate an alternating magnetic field and for measuring an induced signal from said sample, said signal being generated by said alternating magnetic field,   means for generating said alternating magnetic field,   means for moving said sample to discrete locations along a helical path within said static magnetic field, and   means for recording said induced signal from said discrete locations.   
     
     
       2. The apparatus of claim 1 including means for rendering said static magnetic field substantially homogeneous, said means comprising a cylinder having mounted thereon a plurality of electrically conducting coils designed to zero out at least the first six orders of the spherical harmonic expansion of gradient of said static magnetic field. 
     
     
       3. Apparatus for homogenizing a static magnetic field generated by a static magnet which comprises: a liquid sample mounted on a magnetic field probe adapted to generate an alternating magnetic field and for measuring an induced signal from said sample, said induced signal being generated by said alternating magnetic field,   means for generating said alternating magnetic field,   a cylinder positioned within said static magnetic field having mounted thereon a plurality of electrically conducting coils designed to zero out at least the first 6 orders of the spherical harmonic expansion of gradient of said static magnetic field,   means for moving said sample to discrete locations along a helical path within said static magnetic field, and   means for supplying current to said coils to zero out said gradients in response to said induced signal.   
     
     
       4. The apparatus of claim 1 wherein said helical path has a pitch of between about 1 and 5 mm per rotation. 
     
     
       5. The apparatus of claim 2 wherein said helical path has a pitch of between about 1 and 5 mm per rotation. 
     
     
       6. The apparatus of claim 3 wherein said helical path has a pitch of between about 1 and 5 mm per rotation.